let s = 'a'
let n = 123
let f = false
let u = undefined
let nu = null

console.log(Boolean(s)); //ture
console.log(Boolean(''));//false 字符串里面只有空字符串是false
console.log(Boolean(n));
console.log(Boolean(0)); //可描述的数字里面只有0是false 其他都是ture
console.log(Boolean(-1));
console.log(Boolean(NaN)); //NaN是不可描述的数字
console.log(Boolean(undefined));//false
console.log(Boolean(null));//false
console.log(Boolean(false));//false
console.log(Boolean());


console.log(Number('123'));
console.log(Number('abc'));//NaN
console.log(Number(''));//0
console.log(Number('a123'));
console.log(Number());

function add(x,y){
    return x+y;
}
add('1',2)

console.log(String(n));




